The few times I was on CB, the model had the room muted so you had to have at least one token in order to chat. In addition to that, she charged for PMs per visit. It was only a few tokens. But, you had to tip it, with a tip note requesting. Or, unless she initiated it, I think.
I generally don't PM with models unless it's ones I know and am regulars with. But, even then, it's rare as I like to be more engaged with the room as it helps the model out with her room and keep things flowing. If it's a side conversation, I usually try to keep it short so as to not distract her from the room. If I happen to go into a new room, and the models PMs me, I'll respond similarly in that it's a short conversation.
I have no issues paying to PM/friend's lists to models, as it's nice to have the option if needed. But, again, rarely and I have no problems with tip notes. Especially if it's during a tease, flirting, or just making a silly/stupid comment to something she's doing in the room.